1. Field of Invention
This invention relates to hydroponic systems, specifically to an improved method and apparatus for the delivery of nutrient solution to plants.
2. Background of the Invention
Hydroponic systems are designed to apply nutrient solution to plants at a controlled and predictable rate over time. Air-lift pumps, or water pumps driven by compressed air have been used in hydroponic systems before, but in configurations that have made them impractical and unreliable. Air-lift pumps have characteristics beneficial to their use in hydroponic systems. For example, air-lift pumps aerate nutrient solution and deliver nutrient solution to plants simultaneously, favorably contributing to the efficiency and performance of a hydroponic system. Also, an air-lift pump has no moving parts, and is therefore very reliable when used in an operating environment free of objects or accumulations that may clog the pump. Despite this, previous hydroponic systems using air-lift pumps have suffered from many disadvantages, including low reliability, accessibility, viewability, poor performance, high maintenance requirements, and difficulty expanding system size to accommodate many air-lift pumps over a large area.
U.S. Pat. No. 4,676,023 presents a hydroponic system that uses one air-lift pump placed in a nutrient reservoir to deliver hydroponic nutrient to a trough holding a number of plants. This design has a number of real and potential shortcomings. The number of plants that can be grown using this system is limited in that air-lift pumps do not move fluid well across horizontal distances, therefore any application of hydroponic nutrient must be located close to the nutrient reservoir. Another disadvantage of this system is that the plants do not receive freshly air-lifted and oxygenated nutrient over the tops of their roots, but instead gather nutrient from the bottom of the channels in which they sit, thereby lessening oxygen available to the plants' roots, and limiting growth.
U.S. Pat. No. 5,557,885 discloses a method using air-lift pumps. This hydroponic system uses individual “planters”, each composed of two receptacles, or tubs, one of a shorter height than its counterpart. The shorter tub is placed on and into the top of the taller tub. Rocks or other growing media are placed in the upper tub. An air-lift pump is placed vertically within both tubs, sitting within the growing media, through a hole cut in the bottom of the upper tub, and in the space created between the bottoms of the two tubs. This space between the bottoms of the two tubs then, acts as a nutrient reservoir for the air-lift pump. Compressed air is supplied to the air-lift pump and nutrient solution circulates to the top of the growing media, down through the growing media, through holes in the bottom of the upper tub, and back into the reservoir. This system suffers from a number of disadvantages:
(a) The placement of the air-lift pump within each planter makes it vulnerable to clogging from plant roots and debris, making the system unreliable. Organic matter and plant roots grow down through the holes in the bottom of the upper tub, and into the air-lift intake, rendering it inoperable.
(b) There is no practical way to see if debris and organic matter are invading the air-lift pump. The air-lift pump is hidden within the planter unit.
(c) The air-lift pump is not easily accessible should it need to be cleaned, unclogged, or inspected.
(d) The nutrient reservoir formed by this planter cannot hold a large quantity of nutrient solution, and may therefore require frequent replacement, especially when used with fast growing plants.
(e) This system does not automatically maintain a constant nutrient solution level within the planter. As nutrient solution is used up, the nutrient solution level within the planter lowers, creating a number of undesirable conditions. Firstly, the performance of an air-lift pump largely depends on the pump being surrounded with fluid at an optimal, predetermined level. Because the level of nutrient solution in this system changes constantly as it is used up, so too the air-lift pump performance changes accordingly. Additionally, as the nutrient solution level decreases, the salinity and Ph value of the remaining nutrient solution quickly changes, compromising plant health and growth.
(f) There is no means of connecting these planters to external reservoirs.
Hydroponic systems using air-lift pumps are sold today in retail stores under various brand names such as “WaterFarm” and “PowerGrower”. These planters are very similar to U.S. Pat. No. 5,557,885 with a few differences. The shape and size of these planters are usually shorter and wider than said patent. Also, the air pumps are located outside the planter tubs. Finally, in each of these planters, a hose is connected to the base of the lower tub, which allows the planter to be connected to an external reservoir. Although each planter can be connected to a larger, external reservoir to replenish used nutrient and maintain a constant water level, these planters do not, and cannot be made to recirculate nutrient solution between themselves and the external reservoir. Theese planters instead, are merely “topped up” by the external reservoir, as the plants transpire the water in the nutrient solution. As a result, the relatively small quantity of nutrient solution contained in each planter unit quickly degenerates in quality. The only way to maintain nutrient solution quality with this system is to drain and replace the nutrient solution often, thereby contributing to high maintenance requirements. Additionally, these systems suffer many of the same shortcomings as U.S. Pat. No. 5,557,885 such as a vulnerability of the air-lift pump to clogging, and a lack of viewability of the air-lift pump.